Dementia: Update for the Practitioner

There are various neurological disorders that cause dementia. The Diagnostic and Statistical Manual of Mental Disorders (DSM) of the American Psychiatric Association defines dementia as a condition that "must include memory impairment and at least one other cognitive disturbance." This does not allow diagnosis of certain other dementias that differ from Alzheimer's disease. The definition in the Merck Manual better conveys the essence of what we mean by dementia, which is that it doesn't necessarily involve memory. Nearly all dementias do involve memory once they become sufficiently advanced, but in the earliest stages of some of the non-Alzheimer's disorders, memory may not be noticeably affected. In some of these disorders, the cognitive decline is characterized by other abnormalities of thinking, not necessarily involving memory.

We may categorize dementia, like any other medical condition, by etiology. As physicians we find that thinking about the cause of a disease and the pathogenetic processes allows us to best determine mechanisms underlying the disease, predisposing factors, and importantly, the biological underpinnings that may provide clues as to treatment strategies.

Categorized in this fashion, the primary neurodegenerative disorders include Alzheimer's disease, which is the most common such disorder, as well as frontotemporal dementia, Lewy-body dementias, Parkinson's disease dementia, progressive supranuclear palsy, corticobasal degeneration, Huntington's disease, Wilson's disease, and might also include Creutzfeldt-Jakob disease.


	Causes of Dementia Primary neurodegenerative disorders: AD, FTD, DLB, PD, PSP, HD, WD, CJD Vascular: multi-infarct, Binswanger's, CADASIL Inflammatory: multiple sclerosis, vasculitis Infectious: syphilis, Lyme, HIV, other viral, fungal Cancers: primary, metastatic, paraneoplastic Other/physical: hydrocephalus, trauma

	The primary neurodegenerative disorders, divided by biology. Courtesy of Dr. Lawrence Honig

Vascular, inflammatory, and infectious causes of dementia are present in a higher proportion of cases in younger people. Other causes of dementia include neoplasms, whether primary, metastatic or acting at a distance, and physical causes of dementia, such as brain injury or hydrocephalus. I will focus here on the dementias that are more common among the non-Alzheimer's causes.

In various series, examining frequencies of dementing disorders in the elderly at autopsy, Alzheimer's disease is the most common, present in 65 to 85 percent of dementias. Autopsy series are somewhat predisposed to take cases that are more unusual, so Alzheimer's disease may be even more common than this, since autopsies may be more often requested when a patient does not appear to have typical Alzheimer's disease.

While a minority of cases, the non-Alzheimer's dementias, are nonetheless an important set of disorders, which need to be recognized to allow proper diagnosis. Proper diagnosis is comforting and helpful for the family, when trying understand why a loved one has a condition that seems different from others with dementia. Furthermore, different dementias have genetic and prognostic features and different treatment and management considerations.

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